FIND Return a indices of samples with specific property values

     I=FIND(A,CLASSES)
     I=FIND(A,PROP,VALUES,PROP2,VALUES2,...)

 INPUT
     A         SDDATA object
     CLASSES   Cell array with class names
     PROP      Property name (e.g. 'patient')
     VALUES    Category names or indices

 OUTPUT
     I         Indices of samples with specified property values(s)

 DESCRIPTION
 FIND method returns indices of data set samples based on label values.
 The simplest use is to retrieve a find of classes by specifying their
 names in CLASSES. General syntax allows us to define a property PROP and
 VALUES either by string names or by indices.  Indices of samples with any
 of the VALUES are returned (logical OR). When combining multiple
 selections, an intersection (logical AND) is adopted.

 EXAMPLE
 Returning indices of cancer samples from the first five patients:
   I=find(a,'class','cancer','patient',1:5)